Automated institutional and industrial ware-washing machines are generally configured with one wash tank for maintaining a readily available supply of a cleaning solution for use in the machine. During normal usage at least a portion of the cleaning solution is discarded in order to keep the remaining cleaning solution as clean as possible. Fresh water or other clean recycled water is then added to the wash tank to maintain an appropriate liquid level, thereby diluting the concentration of detergent in the cleaning solution. To maintain the cleaning solution at the most efficient cleaning concentration, a measured amount of a concentrated aqueous detergent solution is periodically added to the wash tank by an auxiliary detergent dispenser to form a cleaning solution of the desired strength.
Automated institutional and industrial ware washing machines may also be constructed to add a rinse aid to the rinse water from an auxiliary dispenser to promote sheeting and reduce water spotting on the washed ware.
Automated institutional and industrial fabric washing machines typically create a new cleaning solution for each cleaning cycle to which is added detergent, bleach, fabric softener and other optional additives. Typically, these fabric washing additives are added to the wash water by auxiliary dispensers.
Chemical dispensers used in the processes described above typically have been designed for automatic or semi-automatic operation. Automatic dispensers eliminate the need for constant operator attention to the cleanliness of the wash water and concentration of chemical in the wash tank. Further, automated dispensers minimize operator error due to operator misjudgment in timing or in the amount of chemical to be added, and provides greater accuracy in maintaining the optimum concentration level of chemical in the system.
A number of different techniques have been developed and used for converting solid chemicals used in cleaning processes into a concentrated solution. The majority of such devices have been designed to convert solid powdered detergent. See for example Daley et al, U.S. Pat. No. 3,595,438, issued July 27, 1971; Moffet et al, U.S. Pat. No. 4,020,865, issued May 3, 1977; and Larson et al, U.S. Pat. No. 4,063,663, issued Dec. 20, 1977. For this reason the background of chemical dispensers will be further discussed with respect to the dispensing of a detergent.
One common detergent dispenser technique for converting powdered detergent, is the so-called "water-in-reservoir" type. In the water-in-reservoir type dispenser, the powdered detergent is completely submerged in an aqueous solution. A stand-pipe, usually located near the center of the dispenser tank, maintains a constant level of concentrated solution within the dispenser tank. As water is added to the dispenser tank, a concentrated, often saturated detergent solution or slurry is formed by the swirling action and agitation of the powdered detergent. The added water also causes a portion of the solution or slurry in the reservoir to flow into the stand-pipe, which directs the concentrated detergent solution to the wash tank of the washing apparatus. Such a dispensing technique is generally not practical for dispensing powdered detergents containing incompatible components (such as an active chlorine source in combination with a defoamer) as the incompatible components tend to react upon contact when in solution. Further, there are possible safety hazards involved with the use of such dispensers. Charging or recharging of water-in-reservoir type dispensers requires an operator to place detergent directly into standing water. Since water-in-reservoir type dispeners are typically mounted at about eye level or higher with respect to the operator, any splashing or splattering caused by adding the detergent directly into the concentrated solution poses the danger of spilling concentrated detergent solution onto the eyes, face and skin of the operator. This is particularly hazardous when adding highly alkaline or other such hazardous chemicals.
Another technique for converting a powdered detergent into a concentrated detergent solution involves pouring the powdered detergent onto the convex side of a conical or hemispherical screen having a mesh size smaller than the powdered detergent particles supported thereby. The powdered detergent which directly overlies the support screen is dissolved as needed by a fine mist or spray of water from a nozzle disposed below and on the concave side of the screen. The concentrated detergent solution formed by the action of the water falls by gravity into an underlying reservoir, or is directed by a conduit to the wash tank of a washing apparatus. (See, for example, U.S. Pat. Nos. 3,595,438 issued to Daley et al; 4,020,865 issued to Moffat et al; and 4,063,663 issued to Larson et al.) This technique solves many of the problems associated with the water-in-reservoir type of dispenser as (i) the entire charge of powdered detergent is not wetted, and (ii) an operator loading detergent into the dispenser is not placing detergent directly into standing water and therefore is not subjected to possible boil-over or splattering of the detergent solution.
While the powdered detergent dispensers such as described by the Daley, Moffat and Larson patents have represented significant contributions to the art of detergent dispensing, the use of powdered solid detergent in general has a number of drawbacks in commercial applications. Due to increased sanitary standards and demands for shorter wash times, recently developed detergents have relatively more complex compositions that are more hazardous to the user, less stable, and more difficult to dissolve in a satisfactorily uniform manner. Powdered detergents generally dissolve readily because of their high specific surface areas. However, when such powdered detergents include a mixture of a number of components having relatively different dissolving rates, the detergent is susceptible to differential solubility problems in automatic detergent dispensers; the extent of the solubility problem depending upon the rate of dispensing and the residence (dwell) time of contact between the detergent powder and the dissolving liquid. Those particles having a greater rate of solubility and/or a greater specific surface tend to dissolve first, whereas those having a lower solubility rate and/or a lower specific surface tend to dissolve last.
Another problem associated with powdered detergents is the incompatibility and/or instability of particular detergent components required for good cleaning action, when these components are combined in a powdered detergent composition.
Still another problem inherent in powdered detergent is segregation of different sized and/or weighted particles during manufacturing, shipping and handling. Even when uniform distribution can be achieved during manufacture, subsequent shipping and handling may cause segregation, leading to non-uniformity in the composition of the detergent when it is withdrawn from the container.
A further disadvantage of powdered detergents is that they are quite susceptible to spillage.
Another form of solid detergent is the detergent briquette which comprises pre-shaped briquettes of solid detergent. Dispensing systems for dissolving detergent briquettes are known in the art. See, for example, U.S. Pat. Nos. 2,382,163, 2,382,164 and 2,382,165 all issued Aug. 14, 1945 to MacMahon, and U.S. Pat. No. 2,412,819, issued Dec. 17, 1946 to MacMahon. In the MacMahon systems, the detergent briquettes are dispensed from a modified water-in-reservoir type dispenser wherein a number of the briquettes are held in a mesh basket forming a slot across the diameter of a reservoir. A stream of water directed against the lowermost briquette, in combination with the swirling action of the water engaging the submerged portion of the lower-most briquette, provides the dissolving action. The primary advantage of using detergent briquettes in such dispensers is that the user can visually determine when the detergent dispenser reservoir requires additional detergent. As with the water-in-reservoir dispensers, however, water is left standing in the reservoir, and a portion of the briquettes are submerged within that water. Accordingly, where there are incompatible components within the detergent briquettes, there can be undesirable interaction therebetween. Further, if the detergent contains a defoamer, that defoamer tends to float to the top of the reservoir during periods of inactivity, forming a slag at the water surface. For these and other reasons, the briquette detergent approach has not attained that degree of commercial success in the conventional institutional and industrial washing machine art as has the powdered detergent dispensing approach.
Still another, more recent, form of solid detergent is the "cast" or block form, comprising detergent cast within a mold or container. Dispensing systems for these solids are known in the art. See, for example, U.S. Pat. No. 426,362 issued to Copeland et al and commonly owned U.S. Pat. Nos. 4,569,781 and 4,569,780, issued Feb. 11, 1986 to Fernholz et al. The cast detergent is dispensed by spraying a solvent onto the detergent block within the container, thereby dissolving the exposed surface of the detergent to form a concentrated working solution. The concentrated working solution falls into a reservoir or is directed by a conduit to the wash tank of a washing apparatus. When the chemical compound within the container is completely utilized, the exhausted container is simply discarded and a fully charged container placed in the dispenser.
The use of solid cast detergents has presented great innovations to the dispensing of chemicals used in the cleaning process but additional features have been sought by users of solid block dispensers including (i) the ability to provide a relatively constant chemical dispensing rate, and (ii) a reduced unit cost of the chemical.
Containers utilized for storing and dispensing of solid chemicals used in cleaning processes depend upon the form of the solid detergent. Flaked or granular chemicals are typically packaged in sturdy paper board containers treated to prevent the passage of moisture into the package. Typically, the granular chemical is dispensed from the box by either (i) ripping a hole in the box or (ii) opening a reclosable spout provided on a side panel of the box. This type of container is unsuitable for nonflowing, solid block wash chemicals.
Containers for solid tablet or briquette chemicals used in cleaning processes typically take the form of paper or plastic wrappers which completely surround the tablet or briquette. The chemical is dispensed by removing the wrapper entirely and placing the tablet or briquette into the dispenser. The drawbacks associated with this type of container are: (i) they require physical contact of the skin with the chemical which should be avoided, and with some cleaning compositions such as highly alkaline compounds, can cause severe "burns", and (ii) the chemical must be formed in one step and packaged in a second step, requiring additional time and expense for packaging.
Solid, cast chemicals used in cleaning processes are preferably cast in a sturdy solid plastic container which can act as a mold, a shipping and storage container, and a dispenser housing. The cast chemical may be dispensed by inverting the container over a spray nozzle and impinging solvent directly into the container and onto the exposed surface or surfaces of the chemical contained therein.
Hazardous chemicals used in cleaning processes such as highly alkaline detergents are preferably packaged such that they can be dispensed without coming into physical contact with the human body. The paper and/or plastic wrappers typically utilized with tablet and briquette solid detergents are not adequate for this purpose as they require a large amount of handling to remove the wrapper and place the tablet or briquette into the dispenser after the wrapper has been removed.
Accordingly, a need exists for a dispensing apparatus which can simply, safely, efficiently and inexpensively dispense a homogeneous, uniform, concentrated chemical solution from a solid block of wash chemical at relatively constant concentrations and in certain applications, a need exists for an inexpensive solid block chemical container which minimizes the possibility of skin contact with the wash chemical; allows the solid wash chemical to be formed and packaged in a single step; and provides for a substantially constant rate of chemical dispensing.